(1) Field of the Invention
The invention is related to a heat control system for a consolidation roller used for the production of fiber reinforced polymers, in particular to a heat control system for an adaptive consolidation roller used for the production of fiber reinforced polymers using an automatic thermoplastic tape laying process.
The terms fiber reinforced polymers, composite materials or composites are applied with corresponding meanings in this document.
(2) Description of Related Art
Composite materials are particularly attractive to aviation and aerospace applications because of their exceptional strength and stiffness-to-density ratios and superior physical properties. One of the major issues for the future is the manufacturing of the composite parts and the automation of the processes. Automation is seen as an option to reduce costs, increase throughput and reduce scrap in composite part manufacturing. Over the last years, the use of robots has expanded and processes like automated fiber placement (AFP) or Automated Tape Laying (ATL) are of major importance.
The ATL process is a lay-up method for advanced composites. Typically, material is applied via a numerically or robotically controlled head. The head includes a spool or spools of tape or fiber, a winder, winder guides, a compacting roller and some other elements. The head may be located on the end of a multi-axis articulating robot that moves around the tool or mandrel to which material is being applied, or the head may be located on a gantry suspended above the tool. Tape or fiber is applied to the tool in courses, which consist of one row of material of any length at any angle. Multiple courses are usually applied over an area or pattern and are defined and controlled by machine control software.
In the case of thermoplastic composites processing, the fiber reinforced tapes are guided towards a mandrel or mold where the thermoplastic resin will be heated by a hot gas torch or more recently by a laser or other heating devices, e.g. ceramic heaters, hot air gun or infrared heaters. The tape with the molten resin is then consolidated under pressure applied by a consolidation roller and cooled down. Temperature is a very important processing parameter as it influences the thermoplastic behavior, e. g. healing, melting, crystallization and degradation and thus the quality of the resulting composite parts, e. g. presence of voids, their consolidation, process induced stresses and viscoelastic deformation of the material.
Standard consolidation rollers made of metallic materials are well-adapted for flat or semi-flat parts but not for the manufacture of three dimensional parts. Therefore form adaptive consolidations rollers made of metallic and/or polymeric materials, more preferably of elastomer, e.g. natural rubber, e.g. latex derivate or neoprene (polychloroprene) have been developed these last years.
The temperature range in which such elastomer consolidation rollers can be used is comprised between 100° C. and 400° C. It is very important that the temperature at the surface of the consolidation roller remains constant and does not increase during the whole process. As the surface of the consolidation roller is exposed to a heat source, the temperature may increase considerably during the many courses that are necessary to manufacture the composite part. Therefore consolidation rollers are usually tempered using fluid cooling system inside.
Using materials presenting a good thermal conductivity, it is possible to cool down the surface of the consolidation rollers and indirectly the tapes in order to avoid an uncontrolled increase of the temperature at the consolidation roller surface. This system cannot be used anymore for form-adaptive consolidation rollers as their elastomer surfaces are thermal isolators. Thus, it is very important to find a solution to avoid an uncontrolled increase of the temperature at the surface of the consolidation roller.
The document U.S. Pat. No. 5,700,347 A discloses a thermoplastic head for laying down a plurality of thermoplastic resin-impregnated tapes to form a composite. A heating assembly provides high temperature heat on demand and provides cooler gas to avoid heat damage when the head is not laying down tape. Unique compression rollers are able to withstand high temperature operating conditions. An actively cooled post-compression foot with cooling fins cools and consolidates laid down tape. The surface of the compression roller of U.S. Pat. No. 5,700,347 A can be cooled using air while the applied tape is cooled using a second element “a post compression foot” presenting cooling fins.
The document WO/2011/006956 A discloses a machine for applying fibers for making composite materials including a compacting roller for applying a strip consisting of at least one planar fiber pre-impregnated with resin on an application surface and a heating system capable of emitting a thermal radiation toward said strip. The compacting roller comprises a rigid central tube provided with radial holes and a cylinder made of a flexible material, elastically deformable, arranged on said central tube, and having fluid communication means for placing said radial holes in fluid communication with the outer surface of said roller.
The surface of the compacting roller is cooled using a thermal control fluid, preferably a gaseous fluid, particularly air which is brought to the surface via holes in the tubular wall of the central tube of the roller and the use of porous material. Thus the compacting roller of WO/2011/006956 is complicated and therefore expensive as it has to be holed or/and coated. Moreover WO/2011/006956 uses a gas cooling method with an effectiveness limited by the gas/air temperature, by the thermal capacity of the gas/air in relevant cases and by the maximal flux that can be used.